Brush holder assembly



Oct. 22, 1963 D. N- $UMMERFIELD BRUSH HOLDER ASSEMBLY Filed July 8, 1960 INVENTQR. flawdflfiam merm id,

United States Patent 3,108,201 BRUSH HOLDER ASdEMBLY David N. Surnmerficid, Glen Ellyn, lilL, assignor to Sldl Corporation, Chicago, Ill, a corporation of Delaware Filed .luly 8, 1960, Ser. No. 41,563 8 fllaims. (Cl. 310-247) hollow brush holder open at one end with the brush in J contact with a commutator of an electric motor, the spring yieldingly tuges the brush against the commutator to establish a good electric contact therebetween. The pigtails are subject to twisting and breakage and when the latter occurs there is nothing to prevent the spring from forcing a worn brush out of the holder with the spring then being permitted to come into contact with parts of the motor and/ or housing whereby to cause a dangerous shorting condition and possibly a live housing. While still widely in use, the cost of this type of assembly has caused some manufacturers to eliminate the pigtail with its relatively expensive soldering operation and to connect a conductor terminal to the brush through a slot in the side of the brush holder. As the slot in the brush holder in this type of assembly is open at the commutator end of the holder, after considerable wear of the brush the spring sometimes forces the worn brush and conductor terminal out of the commutator end of the housing and into contact with either parts of the motor or the housing wherebytto again cause a condition dangerous to an operator.

It is, therefore, the general object of the present in-- vention to provide a new and improved electrically safe brush holder assembly for electric motors.

An important object of the invention is to provide a new and improved brush holder assembly which prevents undesirable contact between the conductor terminal electrically connected to the brush and parts of the motor or motor housing upon removal of the worn brush from the holder.

Another object of the invention is to provide a new and improved brush holder assembly which is inexpensive to manufacture and assemble and which is safe in operation.

Certain other objects of the invention will, in part'be obvious, and will in part appear hereinafter.

For a more complete understanding of the nature and scope of the invention reference may now be had to the accompanying drawings wherein:

FIG. 1 is a side elevational view of a hand operable power tool with parts of the housing brokenaway to show brush holder assemblies embodying the invention;

FIG. 2 is an enlarged top plan view of the brush holder of FIG. 1; I

FIG. 3 is a side elevational view of the same;

FIG. 4 is a front end view of the same;

FIG. 5 is an enlarged vertical section taken generally on line 5-5 of FIG. 1;

PEG. 6 is a vertical section taken generally on the line 6-6 of FIG. 5;

FIG. 7 is a vertical section similar to FIG. 5 showing the terminal member of the conductor retained in the holder against the guard member by the spring after a substantial portion of the brush has been frictionally worn away; and

FIG. 8 is a front end view of the brush holder assembly taken generally on the line 8-8 of FIG. 7.

In FIG. 1, brush holder assemblies ltl embodying the invention are incorporated in a typical hand operable electrical power tool 11. The power'tool 11 includes a housing 12 within which is mounted an electric motor including a rotatable armature 13, a commutator l4 and a drive shaft 15 attached thereto, and a field coil 16. A tool receiving drive member 17 is operably connected in a suitable manner to the drive shaft 15. A rear portion of the power tool housing 12 is shaped to form a hand grip lsinto which extends a power cord 1%. A trigger-like member 20 associated with the hand grip 18 is operable to control an on-and-oif switch (not shown) for controlling the operation of the electric motor. On opposite sides of the commutator 14, the tool housing 12 is formed to provide a pair of generally rectangular recesses 22 which open toward the commutator 14 and which are adapted to receive the brush holder assemblies It).

As best illustrated in FIG. 5, each brush holder assembly Ill includes a brush holder 25 formed of insulating or dielectric material, a coil spring 26, and a generally rectangular elongated carbon brush 27 having a front end portion adapted for electrical contacting en gagement with the commutator 14 and a rear end portion provided with a reduced-in-size tail or terminal portion 28. The brush holder 25 (FIGS. 2, 3 and 4) is in the form of a generally rectangular hollow box-like member having a top wall Ell, a bottom wall 31, side walls 32 and 33, and a rear end wall 34. The front end of the holder 25, which is open, is adapted to be positioned adjacent the commutator 14 when the assembly lift is disposed in one of the housing recesses 22. The top wall 36 of the brush holder. 25 is provided with a centrally positioned longitudinally extending slot 36 which extends from the open front end of the brush holder 25 toward the rear end thereof a distance equal at least to the length of a new, unused carbon brush 27.

The carbon brush 2.7 which is slidably disposed in the jcentral bore' or opening 37 in the brush holder 25 is yieldingly urged into contacting engagement with a commutator 14 by the coil spring '26 which is disposed in the rear end of the brush holder 25 with one end seated against the rear wall 34 thereof and the opposite end fitted over the terminal portion 23 of the brush holder 27. To provide the usual electrical connection between the carbon brush 27 of each of the brush holder ascarbon brush 27 in electrical contacting engagement,

therewith. During operation of the electric motor, the

a forward end of each carbon brush 27 is gradually worn away due to its frictional contact with the commutator 14 with the spring 26 serving to retain the carbon brush .27 in electrical contacting engagement with the commutator 14-. The slot 36 in the brush holder 25 permits the terminal member 39 of the field conductor 38 to move forwardly with the rear endof the carbon brush 27 as the forward portion thereof is gradually worn away.

After a substantial portion of the carbon brush 27has been worn away, there is a'tendency for the commutator 14 to flip the remaining portion of the brush 2.7 out of the brush holder 25 whereupon the spring 26 would normally urge the terminal member 39 of the conductor 38 out of the bore 37 of the brush holder 25 whereby it would be free to whip around within the tool housing 12. In this instance, if the terminal member 39 were to contact the commutator 14 it could cause localized arcing and damage thereto and if it should contact adjacent portions of the tool housing 12 it could render the housing electrically alive and dangerous to an operator. This danger of electrical shock to an operator is of particular importance when the brush holder assembly is used in a hand operable portable electric tool such as the tool 11. To prevent such an occurrence upon inadvertent removal of the remaining portion of a carbon brush 27 from the holder 25, a guard member 41 formed of insulating or dielectric material is provided which extends across the slot 36 at the forward or open end of the brush holder 25 adjacent the commutator 14. In the embodiment of the invention disclosed in the drawings, the guard member 41 is integrally molded as part of the brush holder 25 in a manner well known in the art.

When the brush 27 has been worn away to the extent that the terminal member 39 of the conductor 38 abuts against the guard member 41, as illustrated in FIG. 7, the guard member at prevents further forward movement of the terminal member 39 as well as further forward movement of the carbon brush 27 under the influence of the spring 26. The electric motor will then come to a stop until the worn brush 27 has been replaced by a new brush. Should the remaining portion of the worn carbon brush .27 slip out of the brush holder 25 or be flipped out of the holder 25 by the commutator 1d, the terminal 39 will remain clamped against the guard member 41 by the spring 26 whereby to prevent its coming into contact with either the commutator 14 or any of the adjacent parts of the tool housing 12. Thus, the danger of electrical shock to the operator and damage to the power tool are eliminated.

To insure that the terminal member 39 of the field conductor 38 will be normally retained within the brush holder 25 upon removal of the worn portion of the carbon brush 27 by any means, the slot 36 in the brush holder 25 is preferably formed with a width which is less than the outer diameter of the eye portion of the terminal member 39. Thus, the terminal member 39 can only be inserted through the slot 36 during the initial assembly of the parts of the assembly by manually turning it to a plane substantially 90 from its normal mounted position on the terminal portion 28 of the carbon brush 27. Likewise, the terminal member 39 can only be removed from confinement within the brush holder 25 by manually turning it 90 after the Worn portion of the brush 27 has been removed from the brush holder 25. This latter feature further insures against accidental removal of the terminal member 39 from the brush holder 25 and the danger of possible electrical contact thereof with either the commutator 14 or any portion of the tool housing 12.

It will be understood that certain changes may be made in the construction or arrangement of the brush holder assembly disclosed herein without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a brush holder of the type comprising a generally rectangular hollow body member open at one end and closed at the opposite end and adapted to contain a carbon brush and a spring for resiliently urging the brush outwardly through the open end of the body member, the improvement which comprises, a slot formed in one side of the brush holder intermediate the ends of said one side whereby the terminal end of a conductor extending through the slot and electrically connected to the carbon brush between the brush and the spring is retained in the holder upon removal of the brush as a result of said termi nal end being resiliently held against the end of said slot adjacent the open end of the holder by the spring.

2. in a brush holder of the type comprising a generally rectangular hollow body member open at one end and closed at the opposite end and adapted to contain a carbon brush which is resiliently urged outwardly through the open end thereof by a spring seated wholly within said body member between the closed end thereof and the inner end of the brush, the improvement which comprises, a slot formed in one side of the brush holder intermediate the ends of said one side whereby to permit a conductor terminal member to be inserted through the slot and electricaliy connected to the carbon brush for outward movement therewith, the end of said slot adjacent the open end of the holder serving to retain the terminal member within the body member upon removal of a worn carbon brush therefrom.

3. In a brush holder assembly having a hollow brush holder with a closed rear end and an open front commutator end, a carbon brush slidably mounted therein,

and a spring member disposed wholly within the holder and seated between the closed rear end thereof and the rear end of the carbon brush whereby to resiliently urge the brush forwardly through the open end of the holder, the combination of, a slot formed in a side wall of said holder and extending inwardly from the open front end thereof, a lead-in wire insertable through said slot electrically connectable to said brush for movement there with, and a guard member extending across the open front end of said slot for engagement by said lead-in wire whereby to retain said lead-in wire in said holder upon removal of said brush therefrom.

4. In a brush holder assembly for a rotary electric motor, the combination with an insulated carbon brush holder having a bore closed at one end to receive and form a seat for one end of a spring, a carbon brush slidably mounted in said bore and having an inner terminal portion adapted to be engaged by the other end of said spring in yieldable spring-pressed relationship tending to urge said brush out of said bore, said holder having a slotted portion along one side thereof extending inwardly from its open end for a distance approximately the length of said brush, and an electrical conductor having a termiinal portion insertable through said slotted portion into co-operating electrical connection with said terminal portion of said brush and clampingly held thereto by said spring, of guard means on said holder and across said slotted portion adjacent the open end of the therefrom.

5. In a brush holder assembly having a molded hollow dielectric brush holder with a closed end and an open commutator end, a commutator brush slidably mounted in the holder, and a spring member disposed in the holder and having one end seated against the closed end thereof and its opposite end engageable with the inner end of the brush whereby to resiliently urge the brush outwardly through the open commutator end of the holder, the combination of, a slotted portion in aside Wall of said holder extending inwardly from the open commutator end thereof, a conductor having a terminal member insertable through said slotted portion and electrically connectable to said inner end of said brush and clampable thereto by said spring, and an integrally molded guard member extending across the open commutator end of said slotted portion whereby said terminal member is retained in the holder upon removal of said brush from said holder as a result of being held against said guard member by the action of said spring.

6. In a brush holder assembly for a rotary electric motor, the combination with an insulated carbon brush holder having a bore closed at one end to receive and form a seat for one end of a spring, a carbon brush slidably mounted in said bore and having a reduced-in-size inner terminal portion adapted for engagement by the other end of said spring in yieldable spring-pressed relationship tending to urge said brush out of said bore, said holder having a slot along one side thereof extending inwardly from its open end for a distance approximately the length of said brush, and an electrical conductor having an eye shaped terminal member Wider in one di mension than the width of said slot but extendable therethrough in another plane into co-operating electrical connection on said terminal portion of said brush and clampingly held thereto by said spring, of a guard member on said holder and extending across said slot at the open end of the holder whereby said terminal member is resiliently held against said guard member by said spring and retained within said holder upon removal of said brush therefrom.

7. In combination with an electric motor brush holder assembly including, an insulated holder having a bore closed at one end and open at the other end, a spring disposed in said bore and having one end seated against said closed end thereof, a carbon brush slidably mounted in said bore and having a terminal portion adapted to receive the other end of said spring whereby said brush is resiliently urged outwardly of said bore, said holder having a slotted portion extending longitudinally from its open end, and an electrical conductor having a terminal eye portion insertable through said slotted portion into cooperating electrical connection with the terminal portion of said brush, said terminal eye portion adapted to be clamped between said brush and said spring, the improvement which comprises, guard means to prevent said electrical conductor and its terminal portion from sliding out of said slotted portion upon removal of said brush from said bore through wear or otherwise, said guard means including a bar member extending across the end of said slotted portion adjacent the open end of said holder whereby said conductor terminal portion will be clamped against 6 said bar member by said spring upon removal of said brush from the holder.

8. In a brush holder assembly for a rotary electric motor, the combination of an insulated holder having a bore closed at one end and open at the other end to receive a spring seated against said closed end, a carbon brush slidably mounted in said bore and having a reduced-in-size terminal portion adapted to receive the other end of said spring whereby said brush is resiliently urged outwardly of said bore for electrical contacting engagement with a commutator of the motor, said holder having a slotted portion extending longitudinally from its open end, an electrical conductor from a field portion of the motor having a terminal eye portion wider in one plane than the width of said slotted portion but extendable therethrough in another plane for co-operating electrical connection on the terminal portion of said brush, said terminal eye portion adapted to be clamped between said brush and said spring, and guard means to prevent said electrical conductor and its terminal portion from sliding out of said slotted portion upon removal of said brush from said bore through wear or otherwise, said guard means including a bar member formed across the end of said slotted portion adjacent the open end of said holder whereby said terminal eye portion of said conductor will be clamped between said bar member and said spring upon removal of said brush from the holder.

References Cited in the file of this patent UNITED STATES PATENTS 1,277,394 Dean Sept. 3, 1918 1,401,679 Dillin Dec. 27, 1921 1,506,740 Eaton Sept. 2, 1924 

6. IN A BRUSH HOLDER ASSEMBLY FOR ROTARY ELECTRIC MOTOR, THE COMBINATION WITH AN INSULATED CARBON BRUSH HOLDER HAVING A BORE CLOSED AT ONE END TO RECEIVE AND 